Method and apparatus for controlling hydraulic pump for working machine of working vehicle

ABSTRACT

A hydraulic pump displacement control apparatus for a working vehicle capable of reliably detecting the working vehicle under excavating operation and reducing loss in power is provided. For this purpose, the control apparatus includes a bottom pressure detector ( 45 ) for detecting a hydraulic pressure in a bottom side ( 13 A) of a cylinder ( 60 ) for operating a working machine ( 10 ), a displacement control device ( 41 ) for controlling a displacement of a variable displacement hydraulic pump ( 26 ), and a controller ( 50 ) which determines that an excavating operation starts when a predetermined time elapses with a detection value from the bottom pressure detector at a predetermined value or less and thereafter, the detection value exceeds the predetermined value, and outputs a displacement control signal to reduce the displacement of the hydraulic pump to a predetermined displacement that is smaller than the maximum displacement to the displacement control device.

This application is a U.S. National Phase Application under 35 USC 371of International Application PCT/JP03/13125 filed Oct. 14, 2003.

TECHNICAL FIELD

The present invention relates to a method and apparatus for controllinga displacement of a hydraulic pump for a working machine of a workingvehicle, particularly, a vehicle for construction work.

BACKGROUND ART

For example, in a hydraulic system for driving a working machine of awheel loader which is a vehicle for construction work, there is the casewhere a hydraulic pressure is required, but only a small dischargeamount is required at the time of an excavating operation or the like.If a fixed displacement type hydraulic pump is used in such a case, alarge amount of pressure oil is returned into a tank, and large powerloss is caused. In order to reduce the power loss, there is provided amethod of reducing a pump discharge amount at the time of an excavatingoperation by using a variable displacement type hydraulic pump. As oneexample of this, there is the one disclosed in the U.S. Pat. No.6,073,442. According to this, the method is for controlling the pumpdisplacement to reduce to a predetermined displacement of the maximumdisplacement or less by determining that the working vehicle is underexcavating operation when at least one of the following conditions issatisfied: i) the transmission is in the forward and first speed gearposition, ii) the working machine is in the excavating position and iii)the vehicle traveling speed is at the set speed or lower.

Among the above described conditions, the excavating position of theworking machine is specified as shown in FIG. 13. FIG. 13 is a side viewof a working machine 70 in the excavating position. A base end portionof a lift arm 72 is swingably attached to a vehicle body 71 with an armpin 73, and the vehicle body 71 and the lift arm 72 are connected by alift cylinder 74. When the lift cylinder 74 is extended or contracted,the lift arm 72 swings around the arm pin 73. A bucket 75 is swingablyattached to a tip end portion of the lift arm 72 with a bucket pin 76,and the vehicle body 71 and the bucket 75 are connected via a tiltcylinder 77 and a link device 78. When the tilt cylinder 77 is extendedor contracted, the bucket 75 swings around the bucket pin 76. As for theexcavating position of the working machine 70, the line Y to Y whichconnects the arm pin 73 and the bucket pin 76 is set as the reference,and the case where the lift arm 72 is located below the line Y-Y isdefined as being in the excavating position.

However, in the above described method, the following problems exist.First, when the transmission is in the forward and first speed gear, thepump capacity is reduced to a predetermined displacement which is themaximum displacement or less. However, in this case, excavatingoperation is not always performed, but the working vehicle isapproaching a predetermined place while operating the working machinewith the forward and first speed gear in some cases. In such a case, thespeed of the working machine becomes slow, and the working efficiencysometimes reduces. Depending on the soil property, an operation issometimes performed with the forward and second speed gear, on whichoccasion, the pump displacement is not reduced and therefore, power lossoccurs.

Secondarily, when the vehicle traveling speed is a set speed or lower,the pump displacement is reduced to a predetermined displacement whichis the maximum displacement or less. However, there is the case wherethe working vehicle moves to a destination at the set speed or lowerwhile operating the working machine without performing an excavatingoperation. In such a case, the pump capacity is also reduced, and thespeed of the working machine becomes low, which lowers the workingefficiency in some cases. Thirdly, when the transmission is in theforward and first speed gear, the working machine is in the excavatingposition and the vehicle traveling speed is the set speed or lower, thepump displacement is reduced to the predetermined displacement which isthe maximum displacement or less. At the time of ordinary excavation,the bucket is slightly lifted from the ground to prevent the bucket fromcontacting the ground and increasing the traveling resistance until itcomes just in front of the target object, and the bucket is quicklybrought into contact with the ground just before it thrusts into thetarget object. In this case, the response speed of the working machinebecomes low, and there arises the problem that the operation slows downand the operator feels incompatibility.

DISCLOSURE OF THE INVENTION

The present invention is made in view of the above described problems,and has its object to provide a method and an apparatus for controllinga hydraulic pump for a working machine of a working vehicle, whichreduces pump displacement after reliably detecting that the workingvehicle is under excavating operation and reduces loss in power, andwhich does not reduce operation efficiency or does not give a sense ofincompatibility to an operator.

In order to attain the above described object, a method for controllinga hydraulic pump for a working machine of a working vehicle according tothe present invention is: in a method for controlling a hydraulic pumpfor a working machine of the working vehicle having a cylinder foroperating the working machine and the hydraulic pump for supplyingpredetermined pressure oil to the cylinder, including the steps of;measuring a duration time of a state in which a hydraulic pressure in abottom side of at least one cylinder of the cylinder is at apredetermined value or less; determining that an excavating operationstarts when a predetermined duration time elapses and thereafter, thehydraulic pressure in the bottom side exceeds the predetermined value;setting a displacement of the hydraulic pump at a predetermineddisplacement reduced to be smaller than a maximum displacement; andperforming a control to reduce the displacement of the hydraulic pump tothe predetermined displacement.

According to the above method, it is determined that the excavatingoperation starts when the hydraulic pressure in the bottom side of thecylinder is at the predetermined value or less for the predeterminedtime and thereafter, exceeds the predetermined value, and thedisplacement of the hydraulic pump is reduced to the predetermineddisplacement which is smaller than the maximum. Since the hydraulicpressure in the bottom side of the cylinder is always in the state atthe predetermined pressure or lower for the predetermined time beforethe excavating operation starts, and the hydraulic pressure obviouslydiffers during excavating operation and non-excavating operation, it canbe reliably determined that the working vehicle is under excavatingoperation, and efficient reduction in loss of power can be performed.Since the displacement of the hydraulic pump does not reduce until thebucket is thrust into the target object, it does not happen that theoperator feels incompatibility due to reduction in the operating speed.

The control method may further includes the steps of: determining thatthe excavating operation is finished when forward and reverse traveloperating means of the working vehicle is switched to a neutral orreverse travel position from a forward travel position, on performing acontrol by reducing the displacement to the predetermined displacement;and stopping the control to reduce the displacement of the hydraulicpump to the predetermined displacement.

The control method may further includes the steps of: determining thatthe excavating operation is finished when the hydraulic pressure in thebottom side becomes a predetermined value or less within a first settime previously set from the time of determining the start of theexcavation operation, on performing a control by reducing thedisplacement to the predetermined displacement; and stopping the controlto reduce the displacement of the hydraulic pump to the predetermineddisplacement. According to this method, after it is determined that theexcavating operation starts, when the hydraulic pressure in the bottomside of the cylinder becomes the predetermined value or less within thefirst set time, the excavating operation is not continued, and it isdetermined that the excavating operation is finished, and the pumpdisplacement reducing control is stopped. Therefore, the displacement ofthe hydraulic pump is not reduced to the predetermined displacement atthe time of non-excavating operation, and therefore, the operationefficiency is not reduced due to reduction in the speed of the workingmachine.

The control method may further include the steps of: determining thatthe excavating operation is finished when the hydraulic pressure in thebottom side becomes a predetermined value or less, and a hydraulicpressure state of the predetermined value or less continues for morethan a second set time previously set from the time of determining thestart of the excavating operation, on performing a control by reducingthe displacement to the predetermined displacement; and stopping thecontrol to reduce the displacement of the hydraulic pump to thepredetermined displacement. According to this method, after it isdetermined that the excavating operation starts, when the hydraulicpressure in the bottom side of the cylinder becomes the predeterminedvalue or less and this state continues for more than the second settime, and the pump displacement reducing control is stopped. Therefore,even if the pump displacement reducing control is started by, forexample, an error signal, the error signal is determined in a shorttime, and the control to reduce the displacement of the hydraulic pumpis stopped, thus making it possible to prevent reduction in theoperation efficiency.

The control method may further include the steps of: determining thatthe excavating operation is finished when a height of a bucket of theworking machine becomes a predetermined value or more, on performing acontrol by reducing the displacement to the predetermined displacement;and stopping the control to reduce the displacement of the hydraulicpump to the predetermined displacement. According to this method, whenthe cylinder is operated, the bucket is raised and scoops up the targetobject, and scoops more of the target object into the bucket duringexcavating operation, there is no fear that the rising speed of thebucket becomes fast and operability is reduced.

A first construction of an apparatus for controlling a hydraulic pumpfor a working machine of a working vehicle according to the presentinvention includes: in an apparatus for controlling a hydraulic pump fora working machine of a working vehicle having a cylinder for operatingthe working machine and a variable displacement hydraulic pump forsupplying predetermined pressure oil to the cylinder; a bottom pressuredetector for detecting a hydraulic pressure in a bottom side of at leastone cylinder of the cylinder; a displacement control device forcontrolling a displacement of the variable displacement hydraulic pump;and a controller which inputs a detection value from the bottom pressuredetector therein, determines that an excavating operation starts when apredetermined time elapses with the detection value at a predeterminedvalue or less and thereafter, the detection value exceeds thepredetermined value, and outputs a displacement control signal forreducing the displacement of the variable displacement hydraulic pump toa predetermined displacement that is smaller than a maximum displacementto the displacement control device.

According to the above construction, the displacement of the hydraulicpump is reduced to the predetermined displacement when the predeterminedtime elapses with the hydraulic pressure in the bottom side of thecylinder at the predetermined value or less and thereafter, thehydraulic pressure exceeds the predetermined value. Namely, since it isreliably detected that the working vehicle is under excavatingoperation, and the pump displacement can be reduced to the predetermineddisplacement, the working vehicle capable of effectively reducing lossof power and capable of efficiently operating can be obtained.

Further, in the control apparatus: the controller may input therein adetection signal from operation position detecting means for detectingan operation position of forward and reverse travel operating meansprovided at the working vehicle, and may stop transmission of thedisplacement control signal to the displacement control device when theoperation position is switched to a neutral or reverse travel positionfrom a forward travel position. According to this constitution, when theoperation position of the forward and reverse travel operating means isin a neutral or reverse travel position, transmission of thedisplacement control signal for reducing the displacement of thehydraulic pump is stopped. Therefore, the point of time at which theexcavating operation is finished can be reliably detected, and the pumpdisplacement does not reduce during non-excavating operation.Accordingly, the working vehicle without a fear of reducing the workingefficiency can be obtained.

In the control apparatus: the controller may determine that theexcavating operation is finished when the detection value from thebottom pressure detector becomes the predetermined value or less withina first set time previously set, after determining that the excavationoperation starts, and may stop transmission of the displacement controlsignal to the displacement control device. According to thisconstitution, when the detection value from the bottom pressure detectorbecomes the predetermined value or less within the first set time, it isdetermined that the excavating operation is finished, and transmissionof the displacement control signal of the hydraulic pump is stopped.Therefore, the hydraulic pressure in the bottom side of the cylindertemporarily becomes the predetermined value or more, and when thehydraulic pressure reduces in a short time, the control to reduce thedisplacement of the hydraulic pump to the predetermined displacement canbe stopped. Accordingly, the working vehicle without a fear of reducingoperation efficiency can be obtained.

In the control apparatus: the controller may determine that theexcavating operation is finished when the detection value from thebottom pressure detector becomes the predetermined value or less afterdetermining that the excavation operation starts, and a state at thepredetermined value or less continues for more than a second set timepreviously set, and may stop transmission of the displacement controlsignal to the displacement control device. According to thisconstitution, even if the pump displacement reduction control is startedwith the error signal, for example, the error signal can be determinedin a short time, and the control to reduce the displacement of thehydraulic pump to the predetermined displacement can be stopped.Accordingly, the working vehicle without the fear of reducing theworking efficiency can be obtained.

In the control apparatus: a bucket height detector for detecting aheight of a bucket of the working machine may be included; and thecontroller may input therein the bucket height from the bucket heightdetector after determining that the excavation operation starts, maydetermine that the excavating operation is finished when the bucketheight becomes a predetermined value or more, and may stop transmissionof the displacement control signal to the displacement control device.According to this constitution, when the bucket is raised, scoops up thetarget object, and scoops more of the target object into the bucketduring excavating operation, the pump displacement control is stoppedwhen the bucket is at the predetermined height or more, and thereforethe rising speed of the bucket becomes fast, thus eliminating the fearof reducing operability. Accordingly, the working vehicle without a fearof reducing the operation efficiency can be obtained.

A second constitution of an apparatus for controlling a hydraulic pumpfor a working machine of a working vehicle according to the presentinvention includes: in an apparatus for controlling a hydraulic pump fora working machine of a working vehicle having a cylinder for operatingthe working machine, a variable displacement hydraulic pump forsupplying predetermined pressure oil to the cylinder, a control valvefor controlling a flow rate of pressure oil supplied to predeterminedcylinders in the cylinder and a working machine operating lever, abottom pressure detector for detecting a hydraulic pressure in a bottomside of at least one cylinder of the predetermined cylinders; adisplacement control device for controlling a displacement of thevariable displacement hydraulic pump so that a load sensing differentialpressure that is a differential pressure of a load pressure of thepredetermined cylinders and a discharge pressure of the variabledisplacement hydraulic pump becomes constant; and a controller whichinputs therein a detection value from the bottom pressure detector,determines that an excavating operation starts when a predetermined timeelapses with the detection value at a predetermined value or less andthereafter, the detection value exceeds a predetermined value, andreduces a stroke of the control valve for a maximum stroke of theworking machine operating lever to a smaller predetermined stroke thanthe maximum stroke.

According to the above constitution, when the predetermined time elapseswith the hydraulic pressure in the bottom side of the cylinder at thepredetermined value or less, and thereafter, the hydraulic pressureexceeds the predetermined value, the displacement of the hydraulic pumpis reduced to the predetermined displacement. Namely, since it isreliably detected that the working vehicle is under excavatingoperation, and the pump displacement can be reduced to the predetermineddisplacement, a working vehicle capable of effectively reducing loss ofpower and capable of efficiently operated can be obtained. Since thepump displacement is reduced to the small predetermined displacementthan the maximum displacement by the load sensing hydraulic pressurecontrol, a required flow rate can be ensured irrespective of the load ofthe cylinder, and efficient operation can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a wheel loader which is one example of aworking vehicle having a control apparatus according to a firstembodiment of the present invention;

FIG. 2 is a side view of a working machine of the wheel loader in FIG.1;

FIG. 3 is a graph showing one example of a change in a hydraulicpressure occurring to a bottom side of a lift cylinder in each step at atime of excavating and loading operation of the wheel loader in FIG. 1;

FIG. 4 is a system diagram of the control apparatus of the firstembodiment;

FIG. 5 is a flow chart for explaining a control method of the firstembodiment;

FIG. 6 is a side view of a front part of a wheel loader according to asecond embodiment of the present invention;

FIG. 7 is a system diagram of a control apparatus of the secondembodiment;

FIG. 8 is a flow chart for explaining a control method of the secondembodiment;

FIG. 9 is a system diagram of a control apparatus according to a thirdembodiment of the present invention;

FIG. 10 is a graph for explaining a control method of the thirdembodiment;

FIG. 11 is a graph for explaining a modification example of the controlmethod of the third embodiment;

FIG. 12 is a graph for explaining another modification example of thecontrol method of the third embodiment; and

FIG. 13 is a side view showing an excavating position of a workingmachine of a conventional working vehicle.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of a method and an apparatus forcontrolling a hydraulic pump for a working machine of a working vehicleaccording to the present invention will be described in detail withreference to the drawings.

A first embodiment will be explained below. FIG. 1 is a side view of awheel loader which is one example of the working vehicle. In FIG. 1, aworking vehicle 1 has a rear vehicle body 5 having a driver's cab 2, anengine frame 3 and rear wheels 4 and 4, and a front frame 7 having frontwheels 6 and 6. A working machine 10 is mounted to the front frame 7.Namely, a bucket 12 is swingably mounted to a tip end portion of a liftarm 11 of which base end portion is swingably mounted to the front frame7. The front frame 7 and the lift arm 11 are connected by a set of liftcylinders 13 and 13, and the lift arm 11 swings by extending andcontracting the lift cylinders 13 and 13.

A substantially central portion of the tilt art 14 is swingablysupported at the lift arm 11, and one end portion of the tilt arm 14 andthe front frame 7 are connected by a tilt cylinder 15. The other endportion of the tilt arm 14 and the bucket 12 are connected by a tilt rod16, and when the tilt cylinder 15 is extended and contracted, the bucket12 swings. A power unit 20 is loaded on the rear vehicle body 5. Thepower unit 20 is constructed by an engine 21, a torque converter 22, atransmission 23 capable of switching forward and reverse travel andswitching a plurality of speed gears, a distributor 24, speed reducers25 and 25 for driving the rear wheel 4 and the front wheel 6 and thelike. The engine 21 drives a variable displacement hydraulic pump 26which supplies pressure oil to the lift cylinder 13 and the tiltcylinder 15. Forward and reverse travel operating means 30 is providedin the driver's cab 2. In this embodiment, a set of lift cylinders 13and 13 and the tilt cylinder 15 construct a cylinder 60 for operatingthe working machine 10. However, the cylinder 60 is not limited to this,but the cylinder 60 may be an ordinary cylinder having the function of“operating the working machine of a working vehicle”.

Next, one example of the process steps of excavating and loadingoperation of the wheel loader 1 will be explained.

(1) Forward traveling step: The operator operates the lift cylinder 13and the tilt cylinder 15 to bring the bucket 12 into the excavatingposition, and operates the forward and reverse travel operating means 30to move the vehicle forward to the target object to be excavated andloaded.

(2) Excavating step: The operator thrusts the blade edge of the bucket12 into the target object, and operates the tilt cylinder 5 to tilt backthe bucket 12 to scoop the target object into the buckets 12.

(3) Reverse traveling step: After scooping the target object into thebucket 12, the operator makes the vehicle 1 travel in the reversedirection.

(4) Forward traveling and boom raising step: While making the vehicle 1travel forward, the operator extends the lift cylinder 13 to raise thelift arm 11, and while raising the bucket 12 up to the loading position,the operator makes the vehicle 1 approach the dump truck.

(5) Earth moving step: The operator makes the bucket 12 dump at apredetermined position and loads the target object into the rear deck ofthe dump truck.

(6) Reverse traveling and boom lowering step: The driver lowers the liftarm 11 while making the vehicle 1 travel in the reverse direction, andbrings the bucket 12 into the excavating position.

Excavation and loading are performed by repeating the above describedsteps.

FIG. 2 is a side view showing a state of excavating with the bucket 12.The vehicle 1 is made to travel forward in the direction of the arrow A,the blade edge of the bucket 12 is thrust into a target object Z, andthe blade 12 is tilted back, whereby, a force is applied to the bucket12 in the directions of the arrows B and C. Therefore, a high hydraulicpressure occurs to the bottom sides of the lift cylinder 13 and the tiltcylinder 15. Depending on the operation posture, a force in thedirection of the arrow D is applied to the bucket 12, and in this case,a high hydraulic pressure occurs to the head side of the tilt cylinder15. The hydraulic pressures clearly differ at the time of excavatingoperation and at the time of non-excavating operation. Accordingly, thereference value of the lift cylinder bottom pressure is set, and it canbe reliably determined whether it is under excavation operation or not.Since a high hydraulic pressure also occurs to the bottom side of thetilt cylinder 15, the reference value of the tilt cylinder bottompressure is set, and it can be reliably determined whether it is underexcavation operation or not.

FIG. 3 is a graph showing an example of a change in the hydraulicpressure which occurs to the bottom side of the lift cylinder 13 at eachstep at the time of the excavating and loading operation of the wheelloader 1. The vertical axis in FIG. 3 is a hydraulic pressure at thebottom side of the lift cylinder 13, and the horizontal axis is time. Asshown in FIG. 3, the bottom pressure of the lift cylinder 13 is low inthe forward traveling step, becomes high in the excavating step, andbecomes low when excavation is finished and the wheel loader 1 travelsin the reverse direction. When a predetermined pressure P is set now,the bottom pressure of the lift cylinder 13 is lower than P in theentire range of the forward traveling step while it is very much higherthan P in the entire range of the excavating step, and the difference isobvious. The bottom pressure of the lift cylinder 13 is higher than P inthe reverse traveling step, forward traveling and boom raising step, thefirst half of the earth moving step, and thereafter, it is lower than P.The time of the forward traveling step always exists for several seconds(for example, five seconds). Accordingly, by detecting the point of timewhen the bottom pressure of the lift cylinder 13 becomes higher than Pafter it is lower than the predetermined pressure P for a predeterminedtime (for example, one second), the excavating operation starting pointof time can be reliably detected. It is the most efficient to set thetime when the forward and reverse travel operating means 30 is switchedto the reverse travel as the end of excavating operation and perform thedisplacement reducing control of the hydraulic pump in the excavatingstep between the excavating operation starting point and the excavatingoperation end point.

The method and the apparatus for controlling the hydraulic pump will beexplained hereinafter. FIG. 4 is a system diagram showing one example ofa control apparatus 40. In FIG. 4, a capacity control device 41 isconnected to the variable displacement hydraulic pump 26. A tiltoperation valve 43 connecting to the tilt cylinder 15 and a liftoperation valve 44 connecting to the lift cylinder 13 are interposed ona discharge circuit 42 of the variable displacement hydraulic pump 26. Abottom pressure detector 45 is provided at a bottom side 13A of the liftcylinder 13. The bottom pressure detector 45 is, for example, a pressureswitch. The capacity control device 41 and the bottom pressure detector45 are respectively connected to a controller 50. The controller 50 isconnected to operation position detecting means 31 for detecting theoperation position of the forward and reverse travel operating means 30,and detects whether the transmission 23 is in the forward, neutral orreverse position.

Next, the control method will be explained based on a flow chart in FIG.5. After starting operation, the controller 50 inputs the detectionresult from the bottom pressure detector 45 and determines whether thelift cylinder bottom pressure is the predetermined pressure P or lower,or not in step 101. In the case of NO in step 101, the flow returns tothe previous step to step 101. In the case of YES in step 101, the flowgoes to step 102, and the controller 50 starts time measurement. In step103, the controller 50 determines whether the state in which the liftcylinder bottom pressure is the predetermined pressure P or lower lastsfor a predetermined time (for example, one second) or more, or not. Inthe case of NO in step 103, the flow returns to the previous step tostep 103. In the case of YES in step 103, the flow goes to step 104, andthe controller 50 determines whether the lift cylinder bottom pressureexceeds the predetermined pressure P or not. In the case of NO in step104, the flow returns to the previous step to step 104. In the case ofYES in step 104, the flow goes to step 105, and the controller 50determines that the excavating operation starts.

In step 106, the controller 50 sets a predetermined displacement Q whichis reducing from the maximum displacement Qmax of the variabledisplacement hydraulic pump 26 as Q=α*Qmax. Here, α may be a coefficientdetermined corresponding to the magnitude of the travel drive force andhydraulic force when the wheel loader 1 operates, for example, or may bea coefficient determined in accordance with the soil property or thelike (the kinds such as earth, rock and stone and the like, density,viscosity) of the site where the wheel loader 1 operates, and α isordinarily 0.5 to 0.9. Accordingly, when, for example, α is 0.7, thepredetermined displacement Q is set at the displacement which is 0.7times as large as the maximum displacement Qmax. In step 107, thecontroller 50 outputs a control signal to the displacement controldevice 41 and the displacement of the variable displacement hydraulicpump 26 is reduced to the predetermined displacement. At the point oftime when the excavating operation is finished, the operator operatesthe forward and reverse travel operating means 30 and changes thetransmission 23 to the neutral or the reverse travel in step 108.

In step 109, the controller 50 inputs therein a detection signal fromthe operation position detecting means 31, and determines whether thetransmission 23 is in the neutral or the reverse travel position. In thecase of NO in step 109, the flow returns to the previous step to step108. In the case of YES in step 109, the flow goes to step 110, thecontroller 50 determines the excavating operation is finished and theflow goes to step 111. In step 111, the controller 50 stops the pumpdisplacement control and returns the displacement of the variabledisplacement hydraulic pump 26 to the state before control.

After the controller 50 determines that the excavating operation startsin step 105, it starts time measurement in step 112. In step 113, thecontroller 50 determines whether the time in which the lift cylinderbottom pressure exceeds the predetermined pressure P exceeds the firstset time (for example, one second) previously set or not. Steps 112 and113 are carried out in parallel with steps 106 and 107. In the case ofNO in step 113, the controller 50 determines that the excavatingoperation is not continued, then proceeds to step 110 and determinesthat the excavating operation is finished. In the case of YES in step113, the controller 50 determines that the excavating operation iscontinued, and proceeds to step 108. During this time, the hydraulicpump displacement reducing control is performed.

After the controller 50 determines that the excavating operation startsin step 105, it determines whether the lift cylinder bottom pressurebecomes lower than the predetermined pressure P or not in step 114. Inthe case of NO in step 114, the flow returns to the previous step tostep 114. In the case of YES in step 114, the controller 50 starts timemeasurement in step 115. In step 116, the controller 50 determineswhether the time in which the lift cylinder bottom pressure is lowerthan the predetermined pressure P lasts for second set time previouslyset (for example, 0.5 seconds) or more, or not. Steps 114 to 116 arecarried out in parallel with steps 106 and 107. In the case of NO instep 116, the flow returns to the previous step to step 116. In the caseof YES in step 116, the controller 50 determines that it is not underexcavating operation, then proceeds to step 110, and determines that theexcavating operation is finished.

In the above described explanation, the bottom pressure detector 45 isprovided at the bottom side 13A of the lift cylinder 13, and when thehydraulic pressure in the bottom side 13A of the lift cylinder 13 is thepredetermined value or lower for the predetermined time and thereafter,the hydraulic pressure exceeds the predetermined value, it is determinedthat the working vehicle starts the excavating operation, then thedisplacement of the pump is reduced to the predetermined displacementwhich is smaller than the maximum displacement, but the presentinvention is not limited to this. For example, the bottom pressuredetector is provided at the bottom side 15A of the tilt cylinder 15, andwhen the hydraulic pressure of the bottom side 15A of the tilt cylinder15 is the predetermined value or lower for the predetermined time andthereafter, exceeds the predetermined value, it is determined that theworking vehicle starts the excavating operation, then the displacementof the pump may be reduced to the predetermined displacement which issmaller than the maximum displacement. According to this, it goeswithout saying that the same operation and effect can be obtained.

Next, a second embodiment of the method and apparatus for controlling ahydraulic pump for a working machine of a working vehicle according tothe present invention will be described in detail with reference toFIGS. 6 to 8. FIG. 6 differs from FIG. 1 in the respect that a bucketheight detector 32 is included in the wheel loader 1. FIG. 7 is a systemdiagram showing one example of a control apparatus 40A. The controlapparatus 40A differs from the control apparatus 40 in FIG. 4 in therespect that the control apparatus 40A includes the bucket heightdetector 32. FIG. 8 differs from FIG. 5 in the respect that step 118 isadded. Accordingly, in the explanation in FIGS. 6 to 8, the samereference numerals and characters are given to the same portions asexplained in FIGS. 1 to 5, and the explanation of them will be omitted.

As shown in FIG. 6, the front frame 7 includes the bucket heightdetector 32 for detecting the position of the top surface of the baseend portion of the lift arm 11 with respect to the front frame 7. Thebucket 12 is swingably mounted to the tip end portion of the lift arm 11of which base end portion swingably mounted to the front frame 7 with abucket hinge pin 12P. When a height H of the center of the bucket hingepin 12P from a ground surface GL becomes a predetermined height, forexample, 1.5 m, a signal is issued from the bucket height detector 32.Namely, when the height of the bucket 12 of the working machine 10 isthe predetermined value or higher, the bucket height detector 32 issuesthe signal. The bucket height detector 32 is, for example, a proximitysensor, which issues an electrical signal when the top surface of thebase end portion of the lift arm 11 comes within the predetermineddistance from the proximity sensor. As shown in FIG. 7, the bucketheight detector 32 is connected to the controller 50. The controller 50receives the signal from the bucket height detector 32 and determineswhether the bucket 12 is at the predetermined height or higher, or notas will be described later.

When the blade edge of the bucket 12 is thrust into the target object,the bucket 12 is tilted back by operating the tilt cylinder 15 to scoopthe target object into the bucket 12 in the excavating step as shown inFIG. 6, the bucket 12 is sometimes raised in the direction of the arrowY, scoops the target object and scoops more of the target object intothe bucket 12, by operating the lift cylinder 13. In this case, if thedisplacement control of the hydraulic pump is kept performed, theextending speed of the lift cylinder 13 is low because the dischargeamount of the hydraulic pump is small, and therefore, the rising speedof the bucket 12 is low, thus reducing the efficiency of the operation.Therefore, when the bucket 12 is at the predetermined height, thedisplacement control of the hydraulic pump is stopped to enhance therising speed of the bucket 12 in this embodiment.

Next, the control method of this embodiment will be explained based on aflow chart in FIG. 8. After determining that the excavating operationstarts in step 105, the controller 50 determines whether the height ofthe bucket 12 is at the predetermined value or more, or not by thesignal from the bucket height detector 32 in step 118. Step 118 iscarried out in parallel with steps 106 and 107. In the case of YES instep 118, the controller 50 determines that the excavating operation isnot continued, proceeds to step 110 and determines that the excavatingoperation is finished, then proceeds to step 111. In the case of NO instep 118, the controller 50 determines that the excavating operation iscontinued, and proceeds to step 108. During this time, the hydraulicpump displacement reducing control is carried out.

As described above, according to the second embodiment, the bucket 12 israised, scoops up the target object and scoops more of the target objectinto the bucket 12, by operating the lift cylinder 13 during anexcavating operation. When the bucket 12 is at the predetermined heightor more, the displacement control of the pump is stopped, and therefore,the rising speed of the bucket 12 becomes high, thus eliminating thefear of reducing operability. In this embodiment, a proximity sensor isused as the bucket height detector 32 as one example, but the bucketheight detector 32 is not limited to this. For example, the height ofthe bucket hinge pin 12P of the bucket 12 may be detected by detectingthe angle of the lift arm 11. Further, the height of the bucket hingepin 12P of the bucket 12 may be detected by detecting the stroke of thelift cylinder 13.

Next, a third embodiment 3 of the apparatus for controlling thehydraulic pump for the working machine of the working vehicle accordingto the present invention will be described in detail with reference toFIGS. 9 to 12. FIG. 9 is a system diagram showing one example of acontrol apparatus 40B. In the explanation of the control apparatus 40B,the same parts as in the control apparatus 40 explained in FIG. 4 andthe control apparatus 40A explained in FIG. 7 are given the samereference numerals and characters and the explanation of them will beomitted. In FIG. 9, a displacement control device 41B is connected to avariable displacement hydraulic pump 26B in FIG. 9. The tilt operatingvalve 43 which is connected to the tilt cylinder 15 and a lift operatingvalve 44B which is connected to the lift cylinder 13 are interposed onthe discharge circuit 42 of the variable displacement hydraulic pump26B. The lift operating valve 44B is an electromagnetic proportionalcontrol valve, which is connected to a controller 50B and is operated inaccordance with the magnitude of the lift operating valve signal fromthe controller 50B.

A lift cylinder operating lever 55 which is a working machine operatinglever is connected to the controller 50B, and when the operator operatesthe lift cylinder operating lever 55, the lift cylinder operating signalis transmitted to the controller 50B. The controller 50B outputs a liftoperating signal to the lift operating valve 44B in accordance with thelift cylinder operating signal from the lift cylinder operating lever55, and the controller 50B outputs the lift operating valve signal bychanging the output value of an electric command value i of the liftoperating valve signal at the normal time and at the excavatingoperation time.

A load sensing circuit 42AL for detecting the discharge pressure of thevariable displacement hydraulic pump 26B branches from a dischargecircuit 42A of the variable displacement hydraulic pump 26B, and theload sensing circuit 42AL connects to the displacement control device41B. An outlet pressure detecting circuit 42BL of the lift operatingvalve 44B branches from an outlet circuit 42B of the lift control valve44B, and the outlet pressure detecting circuit 42BL connects to thedisplacement control device 41B. By this constitution, a load sensinghydraulic pressure control is performed. Thereby, the displacementcontrol device 41B performs so-called load sensing control forcontrolling a displacement of the variable displacement hydraulic pump26B so that load sensing differential pressure ΔP which is thedifferential pressure between the discharge pressure of the variabledisplacement hydraulic pump 26B and the outlet pressure (load pressureof the lift cylinder 13) of the lift operating valve 44B becomesconstant. Accordingly, irrespective of the magnitude of the loadpressure of the lift cylinder 13, the flow rate in accordance with theopening area of the lift operating valve 44B can be ensured, and theefficient operation can be performed.

Next, an operation of this embodiment will be explained. The controlcontent of this embodiment is the same as the control flows in FIGS. 5and 8, but the methods of setting the pump reduction displacement instep 106 are different. When the operator operates the lift cylinderoperating lever 55 at the normal time when it is not determined theexcavating operation starts, the electric command value i of the liftoperating valve signal from the controller 50B with respect to the liftcylinder operating signal (stroke of the lift cylinder operating lever55) changes as the solid line as shown in FIG. 10. Namely, at themaximum value LSmax of the lift cylinder operating signal where thestroke of the lift cylinder operating lever 55 becomes maximum, theelectric command value i becomes imax. When the electric command value ibecomes imax, the stroke of the lift operating valve 44B becomes VSmax.Then, the opening area of the lift operating valve 44B becomes maximum,and the pump swash plate angle θ is set as θmax so that the load sensingdifferential pressure ΔP in this state becomes a predetermined fixedvalue to control the pump displacement of the variable displacementhydraulic pump 26B to be Qmax which is the maximum displacement.

When the controller 50B proceeds to step 105 in FIG. 5 and determinesthat excavating operation starts, the flow goes to step 106, and thecontroller 50B sets the pump reduction displacement. Namely, when theoperator operates the lift cylinder operating lever 55 in the state inwhich the excavating operation starts, the electric command value ichanges as the broken line as shown in FIG. 10. Namely, at the maximumvalue LSmax of the lift cylinder operating signal, the electric commandvalue i becomes the reduced value iα (for example, 0.7 times as large asimax), and the stroke of the lift operating valve 44B becomes thereduced stroke VSα (for example, 0.7 times as large as VSmax).

As a result, even if the stroke of the lift cylinder operating lever 55is the maximum, the opening area of the lift operating valve 44B becomesthe reduced opening area to be smaller than the maximum value. As aresult, the displacement control apparatus 41B operates so that the loadsensing differential pressure ΔP becomes a predetermined fixed value,and the control is carried out so that the pump swash plate angle θbecomes the reduced pump swash plate angle θα to be smaller than θmax.As a result, the pump displacement of the variable displacementhydraulic pump 26B becomes the reduced Qα to be smaller than the maximumdisplacement Qmax. In this manner, the control device 40B sets thedisplacement of the variable displacement hydraulic pump 26B as areduced predetermined displacement Q to be smaller than the maximumdisplacement Qmax, namely Q=α*Qmax (=Qα).

When determining that the excavating operation is finished andproceeding to step 111, the controller 50B returns the electric commandvalue i to the lift operating valve 44B to the pattern changing as thesolid line (at the normal time). As a result, at the maximum (maximumvalue LSmax) of the stroke of the lift cylinder operating lever 55, theelectric command value i becomes imax. Since the stroke of the liftoperating valve 44B becomes VSmax as a result, the opening area of thelift operating valve 44B becomes the maximum value, and the displacementcontrol device 41B operates so that the load sensing differentialpressure ΔP becomes a fixed value, and carries out the control so thatthe pump swash plate angle θ becomes θmax. Thereby, the pumpdisplacement control is stopped, and the displacement of the variabledisplacement hydraulic pump 26B returns to the state before control.

This embodiment is the same as the first embodiment and the secondembodiment in the following respects: i) the displacement control of thepump is stopped when the operator brings the forward and reverse traveloperating means into the neutral or reverse travel position after theexcavating operation is finished, ii) the pump displacement reducingcontrol is stopped by determining that the excavating operation is notcontinued when the hydraulic pressure at the bottom side of the liftcylinder becomes the predetermined value or lower within the first settime previously set after it is determined that the excavating operationis started, iii) the pump displacement reduction control is stopped bydetermining that the excavating operation is finished when the hydraulicpressure at the bottom side of the lift cylinder becomes thepredetermined value or lower and this state exceeds the second set timepreviously set, after it is determined that the excavation is started,iv) the displacement control of the pump is stopped when the bucket 12is at a predetermined height or higher when the bucket 12 is raised,scoops up the target object and scoops more of the target object intothe bucket 12, by operating the lift cylinder 13 during the excavatingoperation. The control contents of this embodiment other than the aboveare the same as in the embodiment 1 and embodiment 2, and therefore, theexplanation will be omitted. According to this embodiment as describedabove, the same effect as the embodiment 1 can be also obtained.

FIG. 11 shows the case where the electric command value i of the liftoperating valve signal for the stroke of the lift cylinder operatinglever 55 is in the pattern as the solid line (the normal time) and inthe pattern as the broken line (excavating operation time). In thiscase, the maximum displacement of the variable displacement hydraulicpump 26B is reduced, responsiveness in the intermediate range of thestroke of the lift cylinder operating lever 55 is made low to make theresponsiveness in the fine control range dull, and fine control of thelift cylinder 13 can be facilitated.

FIG. 12 shows the case where the maximum value of the electric commandvalue i of the lift operating valve signal for the stroke of the liftcylinder operating lever 55 is maxed out at the time of excavatingoperation. In this case, only the maximum displacement of the variabledisplacement hydraulic pump 26B is reduced, and the responsiveness inthe intermediate range of the stroke of the lift cylinder operatinglever 55 is not changed, so that it is made possible that theresponsiveness in the intermediate range of the stroke of the liftcylinder operating lever 55 does not change. As a result, a change isnot made in the responsiveness in the fine control range, so that it ismade possible that the speed at which the lift cylinder 13 moves doesnot change, and incompatibility does not occur to the operator.

INDUSTRIAL AVAILABILITY

The present invention is useful as a method and apparatus forcontrolling a hydraulic pump for a working machine of a working vehiclewhich is capable of reducing power loss by reliably detecting that theworking vehicle is under excavating operation, and which does not reduceworking efficiency or gives a sense of incompatibility to the operator.

1. An apparatus for controlling a hydraulic pump for a working machineof a working vehicle having a cylinder arrangement for operating theworking machine, a variable displacement hydraulic pump for supplyingoil at a specified pressure to said cylinder arrangement, a controlvalve for controlling a flow rate of oil supplied to predeterminedcylinders in said cylinder arrangement and a working machine operatinglever, comprising: a bottom pressure detector for detecting a hydraulicpressure in a bottom side of at least one cylinder of said predeterminedcylinders in said cylinder arrangement; a displacement control devicefor controlling a displacement of said variable displacement hydraulicpump so that a load sensing differential pressure that is differentialpressure of a load pressure of said predetermined cylinders and adischarge pressure of said variable displacement hydraulic pump becomesconstant; and a controller which inputs therein a detection value fromsaid bottom pressure detector, determines that an excavating operationstarts when a predetermined time elapses with said detection value at apredetermined value or less and thereafter, said detection value exceedsa predetermined value, and reduces a stroke of said control valve for amaximum stroke of said working machine operating lever to be a smallerpredetermined stroke than a maximum stroke.
 2. The apparatus forcontrolling the hydraulic pump for the working machine of the workingvehicle according to claim 1, wherein said controller inputs therein adetection signal from an operation position detecting means fordetecting an operation position of a forward and reverse traveloperating unit of said working vehicle, and stops transmission of saiddisplacement control signal to said displacement control device when theoperation position is switched to a neutral or reverse travel positionfrom a forward travel position.
 3. The apparatus for controlling thehydraulic pump for the working machine of the working vehicle accordingto claim 1, wherein said controller determines that the excavatingoperation is finished when said detection value from said bottompressure detector becomes the predetermined value or less within a firstset time previously set, after determining that the excavating operationstarts, and stops transmission of said displacement control signal tosaid displacement control device.
 4. The apparatus for controlling thehydraulic pump for the working machine of the working vehicle accordingto claim 1, wherein said controller determines that the excavatingoperation is finished when said detection value from said bottompressure detector becomes the predetermined value or less, afterdetermining that the excavating operation starts, and a state at thepredetermined value or less continues for more than a second set timepreviously set, and stops transmission of said displacement controlsignal to said displacement control device.
 5. The apparatus forcontrolling the hydraulic pump for the working machine of the workingvehicle according to claim 1, further comprising: a bucket heightdetector for detecting a height of a bucket of said working machine,wherein said controller inputs therein said bucket height from saidbucket height detector after determining that the excavating operationstarts, and determines that the excavating operation is finished whensaid bucket height becomes a predetermined value or more, and stopstransmission of said displacement control signal to said displacementcontrol device.
 6. The apparatus for controlling the hydraulic pump forthe working machine of the working vehicle according to claim 1, whereinsaid controller is arranged to measure a duration of time when saiddetection value is at the predetermined value or less.
 7. The apparatusfor controlling the hydraulic pump for the working machine of theworking vehicle according to claim 1, wherein said controller is furtherarranged to output a displacement control signal for reducing thedisplacement of said variable displacement hydraulic pump to apredetermined displacement that is smaller than a maximum displacementof said variable displacement hydraulic pump to said displacementcontrol device after said controller determines that the excavatingoperation has started.
 8. A method for controlling a hydraulic pump of aworking machine of a working vehicle having a cylinder arrangement foroperating the working machine, a variable displacement hydraulic pumpfor supplying oil at a specified pressure to said cylinder arrangement,a control valve for controlling a flow rate of oil supplied topredetermined cylinders in said cylinder arrangement and a workingmachine operating lever, said method comprising: detecting a hydraulicpressure in a bottom side of at least one cylinder of said predeterminedcylinders in said cylinder arrangement; controlling a displacement ofsaid variable displacement hydraulic pump so that a load sensingdifferential pressure that is differential pressure of a load pressureof said predetermined cylinders and a discharge pressure of saidvariable displacement hydraulic pump becomes constant; determining thatan excavating operation starts when a predetermined time elapses withsaid detection value at a predetermined value or less and thereafter,said detection value exceeds a predetermined value; and then reducing astroke of said control valve for a maximum stroke of said workingmachine operating lever to be a smaller predetermined stroke than amaximum stroke.
 9. The method for controlling a hydraulic pump of aworking machine of a working vehicle according to claim 8, furthercomprising: determining that the excavating operation is finished when aforward and reverse travel operating unit of said working vehicle isswitched to a neutral or reverse travel position from a forward travelposition, after determining that the excavating operation starts; andthen stopping control to reduce the stroke of said control valve to thesmaller predetermined amount.
 10. The method for controlling a hydraulicpump for a working machine of a working vehicle according to claim 8,further comprising: determining that the excavating operation isfinished when the hydraulic pressure in said bottom side becomes thepredetermined value or less within a first set time previously set,after determining that the excavating operation starts; and thenstopping control to reduce the stroke of said control valve to thesmaller predetermined amount.
 11. The method for controlling a hydraulicpump for a working machine of a working vehicle according to claim 8,further comprising: determining that the excavating operation isfinished when the hydraulic pressure in said bottom side becomes thepredetermined value or less, after determining that the excavatingoperation starts, and a hydraulic pressure state of the predeterminedvalue or less continues for more than a second set time previously set;and then stopping control to reduce the stroke of said control valve tothe smaller predetermined amount.
 12. The method for controlling ahydraulic pump for a working machine of a working vehicle according toclaim 8, further comprising: determining that the excavating operationis finished when a height of a bucket of said working machine becomes apredetermined value or more, after determining that the excavatingoperation starts; and then stopping control to reduce the stroke of saidcontrol valve to the smaller predetermined amount.
 13. The method forcontrolling the hydraulic pump for the working machine of a workingvehicle according to claim 8, further comprising: measuring a durationof time of a state in which said hydraulic pressure in said bottom sideis at the predetermined value or less.